Download OpenXR Developer Tools. Inside that application, set it as the active runtime, then go to developer options, turn on “Using the latest preview of OpenXR Runtime”, then choose custom render scale and set it to 65% or greater. Then you can choose to activate motion reprojection in the setting below that. I also recommend checking the box that says ‘Display Frame Time Overlay’ to help you with performance benchmarking and troubleshooting.
Also, probably more importantly since you are asking this question, you need to refer to this guide to help you set up your G2 and 3090 for VR flight sim in MSFS2020. It is the most comprehensive store of knowledge on how to get the most out of your set up right now, and will lead you down the path of learning the ins-and-outs of how this VR implementation functions; something you’ll need to learn given the state of the game/early adopter tax of VR and MSFS2020. No doubt a small investment relative to the money you’ve already dropped on your set-up though 